Kinetics and Mechanism of Formation and Acid–Catalyzed Decomposition of the [Co(NH3)4CO3]+ Complex Cation in Aqueous Solution

It has been found that the kinetics of acid-catalyzed hydrolysis of the [Co(NH3)4CO3]+ cation follows the rate law –d ln [complex]/d t = k1K[H+]/(1+K[H+]) (5 °C < T < 25 °C; 0.0543M < [HClO4] < 2.7M and I = 1.0M (NaClO4). The reaction course consists of a rapid pre-equlibrium protonation followed by a rate determining ring opening process and the subsequent fast release of monodentate carbonato ligand. The changes of the absorbance for the acidic aqueous solution of the [Co(NH3)4CO3]+ complex ion proceeded at relevant wavelength in the UV-Vis region and time course of these changes were analysed according to a programme “Glint” for the consecutive first – order reaction with two experimental rate constants kfast and kslow. Finally, the aquation mechanism has been proposed and the effect of ligand coordination mode (bidentate carbonato anion) on complex reactivity has been discussed.